Process for operating a calender and calender

ABSTRACT

Process for operating a calender and a calender. The calender includes a hard roll and a soft roll with an elastic surface, in which the hard roll and the soft roll are arranged to form at least one nip, and a finishing medium application device positioned adjacent the soft roll. The process includes providing a finish on the elastic surface of the soft roll.

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] The present application claims priority under 35 U.S.C. §119 ofGerman Patent Application No. 100 37 835.8, filed on Aug. 3, 2000, thedisclosure of which is expressly incorporated by reference herein in itsentirety.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates to a process for operating acalender with at least one nip that is formed by a hard roll and a softroll with an elastic surface. The invention further relates to acalender with at least one nip that is formed by a hard roll and a softroll with an elastic surface.

[0004] 2. Discussion of Background Information

[0005] Such calenders are used for subjecting a material web passingthrough the nip to increased pressure and optionally to an increasedtemperature as well. In this regard, a compression of the material weboccurs and it is possible to influence certain surface properties suchas gloss and smoothness by treatment in a nip.

[0006] In order to explain the invention, a paper web will be used inthe following as an example of a material web. The calendering of apaper web is also the primary application of the invention. However, theinvention may also be used with other material webs that are treated ina similar manner.

[0007] A nip that is formed by a hard roll and a soft roll with anelastic surface is also referred to as a “soft” nip. Because of thedifferent properties of the two rolls forming the nip, differentsurfaces generally result on both sides of the paper web after it haspassed through the soft nip. The side that was in contact with the hardroll has a very smooth surface. This has the condition that it ispossible to provide the hard roll with a smooth surface. This isdifferent in the case of the elastic roll, whose surface is currentlyprimarily formed by a plastic coating. It is relatively difficult toprovide the plastic with the desired smoothness. As a rule, the surfaceroughness of the plastic is much greater than the surface roughness ofthe hard roll.

[0008] It is known from DE 195 06 301 A1 to form the plastic coating ofthe soft roll in two layers, with the outer layer having a lowerelasticity and a greater hardness than the inner layer. For example, theouter layer can be composed of a silicon rubber. While the surfaceroughness of such a soft roll is relatively low when compared to othersoft rolls, it is possible to discern distinct differences in thesurface properties of the material web treated in the calender.

SUMMARY OF THE INVENTION

[0009] The present invention improves the quality of the material web.

[0010] Accordingly, the instant invention is directed to a process ofthe type mentioned at the outset which also includes the surface of thesoft roll built into the calender is provided with a finish.

[0011] It is assumed that the surface roughness of the soft roll iscaused by pores that form in the plastic. With the aid of the finish,these pores are filled and the roll surface is thus correspondingly madesmooth. However, as in other finished surfaces, it can be observed thata roll treated in such a manner only remains smooth for a certain periodof time. Obviously, therefore, the pores form again in operation, forexample, in that the finish is removed again by a material web passingthrough. If the roll is then provided with the finish in its built-instate, it becomes possible to repeatedly or constantly apply a wearlayer that allows the soft or elastic roll to be very smooth for acertain period of time. This smoothness of the soft roll has a verypositive effect on gloss and smoothness of the material web passingthrough.

[0012] It is particularly preferred for a liquid finishing medium to beapplied to the surface and dried. With the aid of a liquid finishingmedium, an even coating of the surface of the roll with the finishingmedium can be achieved relatively quickly. The term “liquid” used heremay be interpreted broadly. It can also be a pasty medium that is onlyfluid in a limited sense. The finishing medium can also be sprayed on inthe form of a sprayed mist. Finally, it is also possible for thefinishing medium to be initially present in the form of steam and tocondense on the surface of the soft roll. The step of drying isadvisable in order to prevent the passing material web from beingcontaminated with the finishing medium. Moreover, a dried finishingmedium adheres better to the surface.

[0013] It is preferred for the finishing medium to be applied to thesurface while the surface is warm. The warmth accelerates the dryingprocess. The roll is normally warm in operation anyway because theelastic roll is flexed during operation, thus producing warmth.

[0014] Preferably, the finish is polished. In the most simple case, thiscan be accomplished in that the roll is moved past a polishing device,for example, a textile cushion. This further improves the smoothness ofthe surface of the soft roll.

[0015] Preferably, the calender is stopped for maintenance purposes inmaintenance pauses and the finish is applied outside of the maintenancepauses. In other words, the finishing medium can be applied duringoperation of the calender such that the surface finish can already berenewed before it has been worn off to the point that an increasedroughness results.

[0016] It is preferred for the finish to be applied during interruptionsin operation. While such interruptions in operation, for example, as aresult of a tear in the paper web, are not desirable, they cannot alwaysbe prevented. In the case of such an interruption in operation, thecalender must be stopped for a certain time anyway in order to removethe torn paper web, for example. This time can be used for applyingfinishing medium to the surface of the soft roll. However, removal ofthe roll is still not necessary.

[0017] Alternately or in addition to this, the finish can be continuallyapplied. This achieves virtually constant conditions on the surface ofthe soft roll.

[0018] It is particularly preferred for the finish to be applied withthe aid of a material web to be calendered in the nip. For example, thepaper web can be provided with the finishing medium in such a way thatthe paper web deposits the finishing medium onto the surface of the softroll. Of course, there must be compatibility between the paper and thefinishing medium so that the quality of the paper web is not diminished.

[0019] Alternately or in addition to this, provision can also be madefor the finish to be applied during the maintenance pauses. In themaintenance pauses, the calender is stopped, so that the finish can alsobe applied with the aid of humans without any danger.

[0020] More preferably, more than one soft roll is used and apredetermined number of the last soft rolls are provided with finish.This is particularly advantageous when the material web first runsthrough a calender such that one side only comes into contact with hardrolls, while this smoothed side then, as it passes through the rest ofthe calender, is pressed by the soft rolls. If these soft rolls are nowprovided with finish, the quality of this surface will no longer be madeworse, but rather the quality will at least be able to be maintained.

[0021] The present invention is also directed to a calender of the typementioned at the outset that also includes a finishing mediumapplication device arranged at the soft roll. Using the finishing mediumapplication device, it becomes possible to apply finishing medium evento a soft roll that is built into a calender for the purpose of makingthe surface of the soft roll extremely smooth. The application of thefinishing medium can even occur during operation under certainconditions such that the surface can be maintained at a constantquality.

[0022] Preferably, the finishing medium application device has adispenser for fluid or pasty finishing medium. The finishing medium can,for example, be sprayed on or applied in another manner. A finishingmedium that is fluid in a wider sense can be used to attain an evencoverage of the surface of the soft roll.

[0023] More preferably, the finishing medium application device has asmoothing device that follows the dispenser in the rotational directionof the roll. The finishing medium is then smoothed even further.

[0024] Preferably, several nips with hard and soft rolls as well as achangeover nip with two rolls of the same type are provided, with afinishing medium application device being provided at all soft rollsbehind the changeover nip. The material web running through such acalender first comes into contact on one side with only hard, butextremely smooth rolls. The one side of the paper web is thus made verysmooth. However, this side will come into contact with the soft rollswhen it passes through the nips behind the changeover nip such that theglossiness or smoothness of this surface is again destroyed. If afinishing medium application device is assigned to all soft rolls behindthe changeover nip, the surfaces of the soft rolls behind the changeovernip are kept so smooth that a decrease in quality of the surface is notto be anticipated.

[0025] The present invention is directed to a process for operating acalender, the calender having a hard roll and a soft roll with anelastic surface arranged to form at least one nip. The process includesproviding a finish on the elastic surface of the soft roll.

[0026] In accordance with a feature of the instant invention, the finishcan be provided by applying a liquid finishing medium to the elasticsurface. Further, the finishing medium may be applied to the elasticsurface while it is warm.

[0027] According to another feature of the present invention, the finishmay be polished.

[0028] Moreover, operation of the calender includes maintenance pausesfor the purpose of maintenance, and the finish is applied outside of themaintenance pauses. The finish can be applied during the maintenancepauses. Also, the finish can be continuously applied during operation ofthe calender. The finish may be applied via a material web to becalendered in the nip.

[0029] Still further, operation of the calender can include maintenancepauses for the purpose of maintenance, and the finish can be appliedduring maintenance pauses.

[0030] The calender may include a plurality of soft rolls and apredetermined number of the soft rolls are provided with a finish.

[0031] The calender can include a changeover nip formed by two similartype rolls, and the predetermined number of soft rolls can be arrangedafter the changeover nip relative to the web travel direction. The twosimilar type rolls may include two soft rolls.

[0032] The finish can be provided by spraying a finishing medium ontothe elastic surface. The finishing medium may include a liquid siliconrubber. The finishing medium can include a hard wax containingpolytetrafluoroethylene. Further, the finish provided on the elasticsurface can form a more smooth surface than the elastic surface withoutthe finish. The finishing medium may be compatible with the material webto avoid any decrease in web quality. The finishing medium can drybetween an application point and a material web contact point.

[0033] The process may also include monitoring the finished elasticsurface for wear, and, upon finding at least a certain amount of wear,refinishing the finished elastic surface.

[0034] The present invention is directed to a calender that includes ahard roll, and a soft roll with an elastic surface. The hard roll andthe soft roll being arranged to form at least one nip, and a finishingmedium application device is positioned adjacent the soft roll.

[0035] According to a feature of the invention, the finishing mediumapplication device may include a dispenser for dispensing finishingmedia. The finishing media can be one of a liquid or a pasty medium.

[0036] In accordance with another feature of the instant invention, thefinishing medium application device can include a smoothing devicearranged to follow the dispenser in a rotational direction of the softroll.

[0037] Further, the calender can include additional hard rolls, andadditional soft rolls with elastic surfaces. The additional hard rollsand additional soft rolls may be arranged to form additional nips. Atleast two similar type rolls can be arranged to form a changeover nip,and additional finishing medium application devices can be positionedadjacent each soft roll located behind the changeover nip in acalendering direction. The at least two similar type rolls can be twosoft rolls.

[0038] According to still another feature of the present invention, thefinishing medium application device can include a nozzle for sprayingfinishing media onto the elastic surface. Further, the finishing mediacomprises a liquid silicon rubber. Still further, the finishing mediacan include a hard wax containing polytetrafluoroethylene. The finishingmedium application device can be arranged to provide a finish on theelastic surface to form a more smooth surface than the elastic surfacewithout the finish. The finishing media may be compatible with thematerial web to avoid any decrease in web quality. Further still, thefinishing media can dry between an application point and a material webcontact point.

[0039] In accordance with a further feature of the invention, a wearsensor can be arranged to monitor the finished elastic surface for wear.The wear sensor may be coupled to the finishing medium applicationdevice such that, upon finding at least a certain amount of wear, thefinishing medium application device refinishes the finished elasticsurface.

[0040] The present invention is directed to a calender that includes afirst roll stack including at least one first hard roll and at least onefirst soft roll, and a second roll stack including at least one secondhard roll and at least one second soft roll. The at least one first hardroll and the at least one first soft roll are arranged to form at leastone first nip and the at least one second hard roll and the at least onesecond soft roll are arranged to form at least one second nip. At leasttwo similar type rolls are arranged to form a changeover nip, and thechangeover nip is positioned between the first roll stack and the secondroll stack, such that the second roll stack is arranged after the firstroll stack in a calendering direction. A finishing medium applicationdevice is arranged adjacent the at least one second soft roll.

[0041] In accordance with a feature of the present invention, the atleast one second soft roll may include a plurality of second soft rolls,and a finishing medium application device can be arranged adjacent eachof the plurality of second soft rolls.

[0042] The invention is directed to a process for operating a calenderthat includes a first roll stack including at least one first hard rolland at least one first soft roll, and a second roll stack including atleast one second hard roll and at least one second soft roll. The atleast one first hard roll and the at least one first soft roll arearranged to form at least one first nip and the at least one second hardroll and the at least one second soft roll are arranged to form at leastone second nip. At least two similar type rolls are arranged to form achangeover nip, and the changeover nip is positioned between the firstroll stack and the second roll stack, such that the second roll stack isarranged after the first roll stack in a calendering direction. Theprocess includes applying finishing medium to a surface of the at leastone second soft roll.

[0043] According to a feature of the instant invention, the process canalso include smoothing the applied finishing medium.

[0044] In accordance with yet another feature of the present invention,the at least one second soft roll may include a plurality of second softrolls, and the process can further include applying finishing medium toeach of the plurality of second soft rolls. Moreover, the process caninclude smoothing the applied finishing medium on each of the pluralityof second soft rolls.

[0045] Other exemplary embodiments and advantages of the presentinvention may be ascertained by reviewing the present disclosure and theaccompanying drawing.

BRIEF DESCRIPTION OF THE DRAWINGS

[0046] The present invention is further described in the detaileddescription which follows, in reference to the noted plurality ofdrawings by way of non-limiting examples of exemplary embodiments of thepresent invention, in which like reference numerals represent similarparts throughout the several views of the drawings, and wherein:

[0047]FIG. 1 schematically illustrates of a calender in accordance withthe features of the invention; and

[0048]FIG. 2 schematically illustrates a finishing medium applicationdevice according to the invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

[0049] The particulars shown herein are by way of example and forpurposes of illustrative discussion of the embodiments of the presentinvention only and are presented in the cause of providing what isbelieved to be the most useful and readily understood description of theprinciples and conceptual aspects of the present invention. In thisregard, no attempt is made to show structural details of the presentinvention in more detail than is necessary for the fundamentalunderstanding of the present invention, the description taken with thedrawings making apparent to those skilled in the art how the severalforms of the present invention may be embodied in practice.

[0050]FIG. 1 shows a calender 1 with ten rolls 2-11 which are arrangedone above the other in a roll stack. The uppermost five rolls 2-6 form afirst group and the lowermost five rolls 7-11 form a second group. Thetwo groups can also be arranged next to one another. Rolls 2, 4, 6, 7,9, and 11 are so-called “soft rolls,” i.e., they have an elasticcovering 12, while rolls 3, 5, 8, and 10 are embodied as so-called “hardrolls” whose surface is composed of a metal, e.g., steel. Hard rolls 3,5, 8, and 10 have a very smooth surface.

[0051] A paper web 13 is now guided through nips 14-22, each of which isformed by two neighboring rolls, i.e., 2 and 3; 3 and 4; etc. Nips 14-17and 19-22 are formed as so-called “soft nips,” i.e., they are limited byone soft roll and one hard roll. In contrast, middle nip 18 formed as aso-called “changeover nip,” i.e., it is formed by soft rolls 6 and 7.

[0052] Paper web 13 is also guided in the calender by guiding device,such as guide rolls 23, which are only shown schematically.

[0053] Paper web 13 is now guided into the nips formed between rolls 2-6of the first group such that the surface of the web facing upwards uponentry into the calender only comes into contact with hard rolls 3 and 5.Thus, this upper side becomes very smooth. The smoothness of hard rolls3 and 5 is replicated on the surface of the paper web.

[0054] However, after passing through changeover nip 18, this upper sidecomes into contact with soft rolls 7, 9, and 11 of the second group. Asthe surface of soft rolls 7, 9, and 11 normally has a significantlygreater roughness than the surfaces of hard rolls 3, 5, 8, and 10, therelatively smooth upper side of paper web 13 tends to be degraded, i.e.,lose its smoothness.

[0055] To diminish this problem, the present invention provides thateach soft roll positioned behind changeover nip 18 relative to a webtravel direction, i.e., rolls 7, 9, and 11, is provided with a finishingmedium application device 24, 25, and 26. An exemplary illustration offinishing medium application device 26 is shown in an enlarged manner inFIG. 2.

[0056] Finishing medium application device has as spray nozzle 27 thatsprays a liquid finishing medium, e.g., a liquid silicon rubber, in theform of a fine mist onto the surface of roll 11, which is rotating inthe direction of an arrow 28. As roll 11 is warm due to operation of thecalender, the finishing medium dries relatively quickly. Behind sprayingnozzle 27 in rotational direction 28, a smoothing device 29 is arrangedthat smooths the dried finishing medium, i.e., polishes it in a mannerof speaking.

[0057] Instead of the above-mentioned silicon rubber, other finishingmedia, preferably synthetic, can be used to give the surface of rolls 7,9, and 11 an extremely smooth surface. For example, a hard waxcontaining Teflon can also be used as the finishing medium, as isprincipally known from polishing vehicle bodies. The roughness of thesesurfaces is thus practically adapted to the roughness of hard rolls 3,5, 8, and 10. In the exemplary embodiment shown, in which finishingmedium application devices 24, 25, and 26 can apply finishing medium tothe rolls 7, 9, and 11 during operation, the layer of finishing mediumneed not have any “stability,” i.e., it can wear off relatively quicklybecause it is constantly renewed. Under certain conditions, it can alsobe sufficient to apply the finishing medium only in intervals, e.g.,when a certain amount of wear has been ascertained. This can beaccomplished using sensors, which are not shown in detail. A conditionfor such an application of finishing medium is that the finishing mediumeither dries so quickly that a “contamination” of paper web 13 does notoccur or that the finishing medium is compatible to paper web 13, i.e.,does not cause any decrease in quality.

[0058] In another manner of operation, the finishing medium can alwaysbe applied when an interruption in operation occurs. Such aninterruption can be forced, e.g., by a tear of the paper web. In thiscase, the torn paper web must be removed from the calender anyway.During this time, finishing medium can be applied to soft rolls 7, 9,and 11. In this event, the service life of the finishing medium must besomewhat longer.

[0059] Especially in the case of calenders that work offline, it isattractive to always apply the finishing medium when an interruption ofthe normal paper web glazing is necessary, for example during a changeof the paper reels.

[0060] However, it is also more favorable under certain circumstances toapply the finishing medium only when the calender must be stopped formaintenance work. Naturally, all manners of application can be combinedwith one another.

[0061] Finally, the finishing medium can also be supplied with the aidof the paper web, i.e., a patina can be artificially supplied that isconstantly renewed.

[0062] It is noted that the foregoing examples have been provided merelyfor the purpose of explanation and are in no way to be construed aslimiting of the present invention. While the present invention has beendescribed with reference to an exemplary embodiment, it is understoodthat the words which have been used herein are words of description andillustration, rather than words of limitation. Changes may be made,within the purview of the appended claims, as presently stated and asamended, without departing from the scope and spirit of the presentinvention in its aspects. Although the present invention has beendescribed herein with reference to particular means, materials andembodiments, the present invention is not intended to be limited to theparticulars disclosed herein; rather, the present invention extends toall functionally equivalent structures, methods and uses, such as arewithin the scope of the appended claims.

What is claimed:
 1. A process for operating a calender, the calender having a hard roll and a soft roll with an elastic surface arranged to form at least one nip, the process comprising: providing a finish on the elastic surface of the soft roll.
 2. The process in accordance with claim 1, wherein the finish is provided by applying a liquid finishing medium to the elastic surface.
 3. The process in accordance with claim 2, wherein the finishing medium is applied to the elastic surface while it is warm.
 4. The process in accordance with claim 1, wherein the finish is polished.
 5. The process in accordance with claim 1, wherein operation of the calender includes maintenance pauses for the purpose of maintenance, and the finish is applied outside of the maintenance pauses.
 6. The process in accordance with claim 5, wherein the finish is applied during the maintenance pauses.
 7. The process in accordance with claim 5, wherein the finish is continuously applied during operation of the calender.
 8. The process in accordance with claim 7, wherein the finish is applied via a material web to be calendered in the nip.
 9. The process in accordance with claim 1, wherein operation of the calender includes maintenance pauses for the purpose of maintenance, and the finish is applied during maintenance pauses.
 10. The process in accordance with claim 1, wherein the calender includes a plurality of soft rolls and a predetermined number of the soft rolls are provided with a finish.
 11. The process in accordance with claim 1, wherein the calender includes a changeover nip formed by two similar type rolls, and the predetermined number of soft rolls are arranged after the changeover nip relative to the web travel direction.
 12. The process in accordance with claim 11, wherein the two similar type rolls comprise two soft rolls.
 13. The process in accordance with claim 1, wherein the finish is provided by spraying a finishing medium onto the elastic surface.
 14. The process in accordance with claim 13, wherein the finishing medium comprises a liquid silicon rubber.
 15. The process in accordance with claim 13, wherein the finishing medium comprises a hard wax containing polytetrafluoroethylene.
 16. The process in accordance with claim 13, wherein the finish provided on the elastic surface forms a more smooth surface than the elastic surface without the finish.
 17. The process in accordance with claim 13, wherein the finishing medium is compatible with the material web to avoid any decrease in web quality.
 18. The process in accordance with claim 13, wherein the finishing medium dries between an application point and a material web contact point.
 19. The process in accordance with claim 1, further comprising monitoring the finished elastic surface for wear, and, upon finding at least a certain amount of wear, refinishing the finished elastic surface.
 20. A calender comprising: a hard roll; a soft roll with an elastic surface, said hard roll and said soft roll being arranged to form at least one nip; and a finishing medium application device positioned adjacent said soft roll.
 21. The calender in accordance with claim 20, said finishing medium application device comprising a dispenser for dispensing finishing media.
 22. The calender in accordance with claim 21, wherein said finishing media is one of a liquid or a pasty medium.
 23. The calender in accordance with claim 20, said finishing medium application device comprising a smoothing device arranged to follow the dispenser in a rotational direction of said soft roll.
 24. The calender in accordance with claim 20, further comprising: additional hard rolls; additional soft rolls with elastic surfaces, said additional hard rolls and additional soft rolls being arranged to form additional nips; at least two similar type rolls being arranged to form a changeover nip; additional finishing medium application devices positioned adjacent each soft roll located behind said changeover nip in a calendering direction.
 25. The calender in accordance with claim 24, wherein the at least two similar type rolls comprise two soft rolls.
 26. The calender in accordance with claim 20, wherein said finishing medium application device comprises a nozzle for spraying finishing media onto the elastic surface.
 27. The calender in accordance with claim 26, wherein said finishing media comprises a liquid silicon rubber.
 28. The calender in accordance with claim 26, wherein said finishing media comprises a hard wax containing polytetrafluoroethylene.
 29. The calender in accordance with claim 26, wherein said finishing medium application device is arranged to provide a finish on the elastic surface to form a more smooth surface than said elastic surface without the finish.
 30. The calender in accordance with claim 26, wherein said finishing media is compatible with the material web to avoid any decrease in web quality.
 31. The calender in accordance with claim 26, wherein said finishing media dries between an application point and a material web contact point.
 32. The calender in accordance with claim 20, further comprising a wear sensor arranged to monitor the finished elastic surface for wear.
 33. The calender in accordance with claim 32, wherein said wear sensor is coupled to said finishing medium application device such that, upon finding at least a certain amount of wear, said finishing medium application device refinishes the finished elastic surface.
 34. A calender comprising: a first roll stack comprising at least one first hard roll and at least one first soft roll; a second roll stack comprising at least one second hard roll and at least one second soft roll; wherein said at least one first hard roll and said at least one first soft roll are arranged to form at least one first nip and said at least one second hard roll and said at least one second soft roll are arranged to form at least one second nip; at least two similar type rolls are arranged to form a changeover nip; said changeover nip being positioned between said first roll stack and said second roll stack, wherein said second roll stack is arranged after said first roll stack in a calendering direction; a finishing medium application device arranged adjacent said at least one second soft roll.
 35. The calender in accordance with claim 34, wherein said at least one second soft roll comprises a plurality of second soft rolls, and a finishing medium application device is arranged adjacent each of said plurality of second soft rolls.
 36. A process for operating a calender that includes a first roll stack comprising at least one first hard roll and at least one first soft roll, and a second roll stack comprising at least one second hard roll and at least one second soft roll, such that the at least one first hard roll and the at least one first soft roll are arranged to form at least one first nip and the at least one second hard roll and the at least one second soft roll are arranged to form at least one second nip, at least two similar type rolls are arranged to form a changeover nip, which is positioned between the first roll stack and the second roll stack, such that the second roll stack is arranged after the first roll stack in a calendering direction, said process comprising: applying finishing medium to a surface of the at least one second soft roll.
 37. The process in accordance with claim 36, further comprising smoothing the applied finishing medium.
 38. The process in accordance with claim 36, wherein the at least one second soft roll comprises a plurality of second soft rolls, and the process further comprises: applying finishing medium to each of the plurality of second soft rolls.
 39. The process in accordance with claim 38, further comprising smoothing the applied finishing medium on each of the plurality of second soft rolls. 